ich_descriptors_tool: Fix an off-by-one

Change-Id: I008abd78c7c42bf3f17e68c192cd79dd427c5cb5
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/19045
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed